Worldwide, it is estimated that 1.8 billion tonnes of Portland cement are produced annually making it one of the most widely used manmade products on earth. Concrete and other cement-based materials define a major component of the materials used in civil engineering applications such as buildings, bridges, roads and other transportation infrastructures, as well as underground constructions such as cementing a well bore.
Primary cementing is the process of placing cement in the annulus between the casing and the formations exposed to the wellbore. Since its inception in 1903, the major objective of primary cementing has always been to provide zonal isolation in the oil, gas and water wells. To achieve this objective, a hydraulic seal must be created between the casing and cement and between the cement and the formations, while at the same time preventing fluid channels in the cement sheath. Oil and gas cementing service companies have introduced various chemical additives in order to achieve and improve desired properties of cement slurries. Many of such cement additives can cause the slurry to foam during mixing. Excessive slurry foaming can have several undesirable consequences. Slurry gelation can result, and loss of hydraulic pressure during pumping can occur owing to cavitation on the mixing system. In addition, air entrainment may cause undesired slurry densities to be pumped down hole as measured density at surface will be different than actual downhole density increasing the risk of formation damage.
During slurry mixing, a densitometer or mass flow meter is used to help field operators proportion the solid and liquid ingredients. If air is present in the slurry at the surface, the density of the system “cement+water+air” is measured by the densitometer. Since the air becomes compressed downhole, the true downhole slurry density becomes higher than the measured surface density which can damage the formation. Antifoaming or defoaming agents are usually added to the mix water or dry-blended with the cement to prevent such problems. They may also be used for breaking foamed fluids. In such applications, defoamer may be utilized to break the excess foamed fluid returned to surface after well treatment and thus facilitate disposal process. In general, desirable antifoaming or defoaming agents, have the following characteristics to be effective: a) insoluble in the foaming system, and b) lower surface tension than the foaming system. The antifoaming agent functions largely by spreading on the surface of the foam or entering the foam lamella. Because the film formed by the spread of antifoam on the surface of a foaming liquid does not support foam, the foam situation is alleviated.